Abstract
Reducing ventilator-associated lung injury by individualized mechanical ventilation (MV) in patients with Acute Respiratory Distress Syndrome (ARDS) remains a matter of research. We randomly assigned 27 pigs with acid aspiration-induced ARDS to three different MV protocols for 24 h, targeting different magnitudes of collapse and tidal recruitment (collapse&TR): the ARDS-network (ARDSnet) group with low positive end-expiratory pressure (PEEP) protocol (permissive collapse&TR); the Open Lung Concept (OLC) group, PaO2/FiO2 >400 mmHg, indicating collapse&TR <10%; and the minimized collapse&TR monitored by Electrical Impedance Tomography (EIT) group, standard deviation of regional ventilation delay, SDRVD. We analyzed cardiorespiratory parameters, computed tomography (CT), EIT, and post-mortem histology. Mean PEEP over post-randomization measurements was significantly lower in the ARDSnet group at 6.8 ± 1.0 cmH2O compared to the EIT (21.1 ± 2.6 cmH2O) and OLC (18.7 ± 3.2 cmH2O) groups (general linear model (GLM) p < 0.001). Collapse&TR and SDRVD, averaged over all post-randomization measurements, were significantly lower in the EIT and OLC groups than in the ARDSnet group (collapse p < 0.001, TR p = 0.006, SDRVD p < 0.004). Global histological diffuse alveolar damage (DAD) scores in the ARDSnet group (10.1 ± 4.3) exceeded those in the EIT (8.4 ± 3.7) and OLC groups (6.3 ± 3.3) (p = 0.16). Sub-scores for edema and inflammation differed significantly (ANOVA p < 0.05). In a clinically realistic model of early ARDS with recruitable and nonrecruitable collapse, mechanical ventilation involving recruitment and high-PEEP reduced collapse&TR and resulted in improved hemodynamic and physiological conditions with a tendency to reduced histologic lung damage.
Highlights
In patients with Acute Respiratory Distress Syndrome (ARDS) mechanical ventilation with low tidal volumes (VT) can reduce complications such as ventilator associated lung injury (VALI) and mortality [1,2,3]
The mean amount of HCl required for inducing moderate ARDS (ARDSnet 124 ± 20, Open Lung Concept (OLC) 105 ± 30, Electrical Impedance Tomography (EIT) 135 ± 16 mL) differed marginally between groups (GLM p = 0.046, post-hoc: OLC vs. EIT p = 0.045)
Recruitment and subsequent individualization of positive end-expiratory pressure (PEEP) using the entirely noninvasive EIT-method resulted in lung conditions matching those seen in the oxygenation-focused OLC
Summary
In patients with Acute Respiratory Distress Syndrome (ARDS) mechanical ventilation with low tidal volumes (VT) can reduce complications such as ventilator associated lung injury (VALI) and mortality [1,2,3]. Among the advantages of the ARDSnet PEEP/FiO2-table are its straightforward use and the limitation of VT and plateau airway pressure potentially reducing VALI Another approach to reduce VALI is based mainly on physiological rationale and involves reducing collapse and TR (collapse&TR) by combining lung re-aeration by recruitment maneuvers (RM) and subsequent decremental PEEP-titration along the expiratory limb of the individual pressure–volume curves [5,9,10,11,12,13,14]. If lung collapse was assessed again after commencing mechanical ventilation with the “individualized” PEEP, it was seldom truly minimized or zero, suggesting the presence of nonrecruitable lung tissue [9,10,19]
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